Aircraft need to vary the amount of lift that different sections of their airframe, in particular their wings, produce for take-off, landing and manoeuvring during flight. Generally a number of control surfaces are used to control the flow of air over the airframe of an aircraft. Control surfaces used on an aircraft include slats, ailerons, flaps, and spoilers. For example, flaps are generally deployed symmetrically to control the stalling speed of an aircraft and ailerons are deployed to control the roll of the aircraft by operating asymmetrically, i.e. an aileron on one wing goes down as an aileron on the other wing goes up, such that the aircraft is caused to roll due to an increased lift produced by one wing and decreased lift generated by the other wing. An aircraft generally has additional control surfaces to further control the attitude of the aircraft, such as a rudder mounted to a vertical tail structure which operates to control the yaw of the aircraft, and elevators mounted to horizontal tail structures which operate to control the pitch of the aircraft.
Aircraft control surfaces are generally hingedly mounted to an airframe of an aircraft, for example to one of the wings or tail structures, so that they can pivot relative to the wing or tail structure and change the airflow over the wing or tail structure. A hinge assembly is used to mount the control surface and to rotate the control surface across a range of motion. Such a hinge assembly is able to maintain the control surface in a range of positions relative to the airframe of the aircraft so that positioning of the control surface can be accurately controlled.
A conventional hinge assembly for hingedly mounting a control surface to an airframe of an aircraft comprises a first pivot point defining a longitudinal axis about which the control surface pivots, and a second pivot point which is offset from the hinge point. A hydraulic piston is generally mounted to the second pivot point and extends between the second pivot point and the wing or tail structure so that, when the piston is actuated, the control surface is urged to rotate about the first pivot point due to the moment applied by the piston. Generally a hinge assembly will comprise a plurality of second pivot points and pistons spaced along the length of the control surface so that a uniform movement of the control surface is obtained along its length.
However, a problem with a conventional hinge assembly is that the pistons require a large space to house them, and it is not possible to produce the control surface as a modular unit. Furthermore, such systems require a large number of pistons to operate and a complex hydraulic system.
As described above, ailerons mounted to the wings of an aircraft are deployed to control the roll of an aircraft. However, an issue with the use of conventional ailerons is that as a secondary effect to generating roll, they also generate adverse yaw. Adverse yaw occurs when one aileron is deflected upwards and the other aileron on the opposing wing is deflected downwards to cause the aircraft to roll in the direction of the aileron deflected upwards. However, the ailerons also cause the aircraft to yaw in the opposite direction to the roll, which is known as adverse yaw, and this is normally compensated for by use of the rudder.
However, another means of compensating for adverse yaw, and generally controlling the yaw of an aircraft, is by use of spoilerons. A spoileron is a control surface which upstands from a control surface, such as a wing or an aileron, to spoil the airflow over it and so change the lift generated by the wing. Therefore, a spoileron can be used to compensate for the adverse yaw generated by use of the ailerons, or used in conjunction with the ailerons to allow simultaneous yaw and roll control.
A double acting spoileron is known from U.S. Pat. No. 2,582,348, in which each aileron has opposing spoilerons which are hinged to extend from the upper and lower surfaces of the aileron. Each pair of opposing spoilerons act in conjunction with each other so that they simultaneously extend from or are retracted in the aileron. The spoilerons are rotated by cables which act around two interacting quadrants and which are actuated by a piston. However, problems with the spoileron hinge assembly shown in U.S. Pat. No. 2,582,348 include the achievable chord length of the control surface being reduced due to the required length of the actuating piston, the actuating piston being orientated in the line of flight and the complicated and unreliable arrangement of the cables acting around the two interacting quadrants.
The present invention seeks to provide a hinge assembly for rotatably mounting a control surface on an aircraft which overcomes or substantially alleviates the problems and disadvantages described above.